The Motion Picture Expert Group (MPEG) develops standards concerning audiovisual content. One component of the MPEG standard scheme includes MPEG-7 standards which are directed to providing descriptions of audiovisual content that may be of interest to the user. Specifically, the MPEG-7 standards are developed to standardize information describing the audiovisual content. The MPEG-7 standards may be used in various areas, including storage and retrieval of audiovisual items from databases, broadcast media selection, tele-shopping, multimedia presentations, personalized news service on the Internet, etc.
According to current MPEG-7 standards, descriptions of audiovisual content are divided into structural (or segment) descriptions and semantic descriptions. Structural descriptions describe the audiovisual content from the viewpoint of its structure. That is, the descriptions are structured around segments which represent physical spatial, temporal or spatio-temporal components of the audiovisual content. Each segment may be described by signal-based features (color, texture, shape, motion, audio features, etc.) and some elementary semantic information.
Semantic descriptions describe the audiovisual content from the viewpoints of its conceptual notions. The semantic descriptions involve entities such as objects, events, abstract concepts and relationships. The structural descriptions and semantic descriptions are related by a set of links, which allows the audiovisual content to be described on the basis of both content structure and semantics together. The links relate different semantic concepts to the instances within the audiovisual content described by the structural descriptions.
Semantic descriptions describe entities that are either concrete or abstract. A concrete entity can have an instance in the real world or the media. An abstract entity results from applying abstraction to a physical entity. Various levels of abstraction may be applied to a physical entity when creating a description. For instance, a description may be created as a media abstraction. A media abstraction results from generalizing a media, i.e., the description is not attached to a specific media. A formal abstraction (or a lambda abstraction) is created from a description of a concrete entity by generalizing one or more elements of the entity, i.e., by substituting one or more elements of the entity by a variable. A description may also be created as an abstraction of a higher degree (e.g., a metaphor, an abstraction of abstractions, etc.).
An abstraction can be used as a template for creating descriptions of specific audiovisual items or lower level abstractions. For instance, an archivist who needs to create a catalog of a large number of audiovisual items contained in a digital library can use such templates to create descriptions of these audiovisual items. In another example, existing abstractions can be reused by software when generating new descriptions. However, no mechanism currently exists to indicate that a description is an abstraction and to identify the type of the abstraction (i.e., whether the description is a media abstraction, a lambda abstraction, a metaphor, etc.), thereby complicating a task of creating new descriptions from existing descriptions.